Dogal is in use by Hispanic cowboys in New Mexico. I can't find written verification, but I have heard it used as Chavez y Gilbert states.

The Spanish usage with regard to animals is as a halter, but an old usage is for a slip-knot or lasso- ".....se forma un lazo para atar las caballerias por el cuello." Diccionario de la Lengua Española, Real Academia Española.
Colonial Spanish has largely disappeared in New Mexico, but it was predominant among Hispanics in northern New Mexico until about WW2, when there were many changes to New Mexican Hispanic lifestyles.

A dogie, or motherless calf, was lassoed and branded by whoever found it. It is not a big step from dogal, defined as a lasso, to dogal, a motherless calf caught by a "new owner."